The former CEO of a rocket launch firm has
proposed an audacious plan to send astronauts on a one-way trek to Mars using a
pair of tethered U.S. space shuttles that would parachute to the Martian
surface.

Inventor Eric Knight, a former CEO
of the rocket
firm UP Aerospace, detailed the plan - which he?s billed ?Mars on a
Shoestring? - in a thought exercise designed to encourage unconventional
thinking for future human spaceflight.

?My
thought paper is a mental exercise to encourage new ideas,? Knight told SPACE.com in an e-mail interview. ?I also
hope it spurs a re-evaluation of the timeline for human exploration of Mars.
Twenty years seems like an eternity, given that we were able to get to the moon
in less than 10 years ? and we were essentially doing so ?from scratch.??

NASA?s
current plan for future human spaceflight includes retiring its three aging
space shuttles - Discovery, Atlantis and Endeavour - in 2010, launching their
capsule-based successor Orion by 2015 and returning
astronauts to the moon by 2020. Any push to Mars would come in the decades
that followed under the NASA vision.

Why
wait?

Knight
posted his proposal to the Web site of his Connecticut-based firm Remarkable
Technologies, Inc., where he serves as president. The interplanetary pitch goes
like this:

Instead of mothballing NASA?s aging
shuttle fleet in 2010, two of the orbiters could be launched with SpaceHab?s Research Double Modules in their respective
cargo bays for living space.

The two shuttles would be connected
in orbit - cargo bay to cargo bay - by a truss outfitted with a central rocket
engine to provide the thrust necessary to leave Earth
orbit. An inflatable connecting corridor between the two shuttle airlocks would
provide astronaut access between the linked spacecraft.

Knight likens his plan as an evolved
version of the Mars Direct plan advocated by Mars Society
President Robert Zubrin, which also detailed a
mission that used tethered modules and hinged on a crew?s ability to generate
their return fuel once they arrived at Mars.

Once underway, the spent rocket
engine and its support truss could be jettisoned, and the connecting corridor
and a cable tether linking the two space shuttles to extended outward a few
hundred feet. The shuttles would then fire their thrusters in concert to enter
a gentle spin that could provide slight gravity for the months-long flight
through interplanetary space.

NASA?s space shuttles aren?t built
to support crews for longer than just over a couple weeks at a time, though
Knight suggests that regenerative life support systems like those recently
delivered to the International Space Station could do the trick. Hydroponic gardens inside the living modules would boost
crew food supplies in the plan. Periodic pit stops to resupply
fuel and other expendables would be required along the way, necessitating some
sort of freighter assist, he adds.

Landing challenge

But it?s once the cobbled-together
Mars ship arrives at the red planet that Knight?s proposal takes a novel turn.
Since NASA?s 100-ton space shuttles are designed to glide through Earth?s
atmosphere during landings, they won?t be able to handle well in the thinner
atmosphere of Mars.

Knight suggests using massive
parachutes.

?What I propose is the development
of a very large parachute system that would be stowed in each of the orbiter's
payload bays,? he writes in the paper. ?Each orbiter would then enter the Mars
atmosphere and descend ballistically (like Apollo and
Soyuz capsules), deploy its parachute system, and land wheels down with surely
a pretty good thump - even with the planet's gravity just 38 percent of
Earth's.?

Knight?s proposal is chiefly a
one-way mission, which would call for a unique cadre of astronaut pioneers
willing to become the
first settlers on Mars. More likely, he surmises, the mission could be a
pathfinder that would set the stage for the later arrival of a relief crew
aboard dedicated Marscraft capable of return trips.

There is no return plan and there
are substantial challenges that remain to be solved. For one, NASA?s space
shuttles aren?t shielded against the severe radiation environment, so
countermeasures would have to be developed.

But Knight intends his proposal to
serve not as a technical blueprint, but as a springboard for more creative
ideas for the future of human spaceflight.

Tariq joined Purch's Space.com team in 2001 as a staff writer, and later editor, covering human spaceflight, exploration and space science. He became Space.com's Managing Editor in 2009. Before joining Space.com, Tariq was a staff reporter for The Los Angeles Times. He is also an Eagle Scout (yes, he has the Space Exploration merit badge) and went to Space Camp four times as a kid and a fifth time as an adult. He has journalism degrees from the University of Southern California and New York University. To see his latest project, you can follow Tariq on Google+, Twitter and on Facebook.